scholarly journals An Improved Comprehensive Model of Pyrolysis of Large Coal Particles to Predict Temperature Variation and Volatile Component Yields

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 884
Author(s):  
Wenning Zhou ◽  
Hailong Huo ◽  
Qinye Li ◽  
Ruifeng Dou ◽  
Xunliang Liu
Keyword(s):  
Heat Transfer ◽  
Temperature Variation ◽  
Volatile Component ◽  
Apparent Temperature ◽  
Transfer Model ◽  
Comprehensive Model ◽  
Volatile Yield ◽  
Coal Particles ◽  
Volatile Release ◽  
The Difference

In this work, an improved comprehensive model was developed for large coal particles to predict temperature variation and volatile component yields. The kinetics model of volatile component yields, where the volatile matters were assumed to comprise nine species, was combined with heat transfer model. The interaction between volatile yield and heat transfer during pyrolysis of large Maltby coal particles was investigated. An apparent temperature difference has been observed between the surface and core of particles at the initial heating stage. The non-uniform temperature distribution inside coal particles causes non-simultaneous volatile yields release from the surface and core area. The volatile release occurs after the coal temperature rises higher than 350 °C, and its yield steeply increases within the temperature range of 450–520 °C. The peak of volatile release rate corresponds to about 485 °C due to the rapid release of tar and H2O. The tar is almost completely released at around 550 °C. With the increasing particle size, the difference in temperature and volatile yield between the surface and core increases at the end of heating. The results are expected to provide insights into the interaction between heat transfer and volatile yields during pyrolysis of large coal particles.

scholarly journals The difference in the thermal conductivity of nanofluids measured by different methods and its rationalization

2016 ◽  
Vol 7 ◽  
pp. 2037-2044 ◽  
Author(s):  
Aparna Zagabathuni ◽  
Sudipto Ghosh ◽  
Shyamal Kumar Pabi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Laser Flash ◽  
Flash Method ◽  
Transfer Model ◽  
Measuring Methods ◽  
Order Of Magnitude ◽  
Wire Method ◽  
The Difference ◽  
First Time

A suspension of particles below 100 nm in size, usually termed as nanofluid, often shows a notable enhancement in thermal conductivity, when measured by the transient hot-wire method. In contrast, when the conductivity of the same nanofluid is measured by the laser flash method, the enhancement reported is about one order of magnitude lower. This difference has been quantitatively resolved for the first time on the basis of the collision-mediated heat transfer model for nanofluids proposed earlier by our research group. Based on the continuum simulation coupled with stochastic analysis, the present theoretical prediction agrees well with the experimental observations from different measuring methods reported in the literature, and fully accounts for the different results from the two measuring methods mentioned above. This analysis also gives an indication that the nanofluids are unlikely to be effective for heat transfer in microchannels.

PRECISION OF HEAT TRANSFER MEASUREMENTS WITH THERMOCOUPLES—INSULATION ERROR

1948 ◽  
Vol 26f (12) ◽  
pp. 565-583 ◽  
Author(s):  
W. A. Mohun
Keyword(s):  
Heat Transfer ◽  
Temperature Variation ◽  
Experimental Error ◽  
Specific Conductivity ◽  
Small Diameter ◽  
Critical Distance ◽  
Simple Method ◽  
The Difference

A method has been developed for calculating the temperature variation in insulated thermocouple lead wires that do not follow an isothermal path. The difference between the temperature of the junction and that of the surrounding material that it purports to measure has been called "insulation error." It has been shown that insulation error is determined by variations in the temperature of the path followed by the lead wires only over a limited distance from the junction, which has been called the "critical distance." Hence, to eliminate insulation error the path of the wires need be isothermal only for the critical distance. A simple method has been developed for calculating the critical distance and the insulation error. When the path of the wires cannot be made isothermal the conditions for minimum experimental error are shown to be small diameter wires of low specific conductivity with a minimum of insulation.

Heat Transfer Studies on Lead-Bismuth Eutectic Flows in Circular Tubes

2008 ◽  
Author(s):  
A. Borgohain ◽  
N. K. Maheshwari ◽  
P. K. Vijayan ◽  
D. Saha ◽  
R. K. Sinha
Keyword(s):  
Heat Transfer ◽  
Liquid Metal ◽  
Nuclear Reactor ◽  
Flow Analysis ◽  
Turbulence Models ◽  
Transfer Model ◽  
Flow Through ◽  
Lead Bismuth Eutectic ◽  
The Difference ◽  
Physical Correlations

The use of accurate heat transfer model in liquid metal like Lead Bismuth Eutectic (LBE) flow is essential for the designing of the liquid metal cooled nuclear reactor systems. In the present study, the existing physical correlations for heat transfer in LBE flow through circular tube have been reviewed and assessed with the experimental results. In CFD analysis, PHOENICS-3.6 is used to carry out the evaluation of the various turbulence models in the tube geometry and to identify the difference between the numerical results and experimental ones in LBE flows. Based on the assessment of the existing correlations for heat transfer in LBE flow and the CFD results achieved, the best-suited correlation for turbulent Prandtl number is recommended in terms of Peclet number. This Prt can be incorporated in PHOENICS for LBE flow analysis.

Influence of Freestream Vortical Structures on Stagnation Region Heat Transfer

2000 ◽  
Author(s):  
Aung N. Oo ◽  
Chan Y. Ching
Keyword(s):  
Heat Transfer ◽  
Leading Edge ◽  
Heat Transfer Model ◽  
Transfer Model ◽  
Vertical Orientation ◽  
Stagnation Region ◽  
Stagnation Line ◽  
Vortical Structures ◽  
Horizontal Orientation ◽  
The Difference

Abstract An experimental study was performed to investigate the influence of freestream vortical structures on stagnation region heat transfer. A heat transfer model with a cylindrical leading edge was tested in a low speed wind tunnel at Reynolds numbers ranging from 67,750 to 142,250 based on leading edge diameter of the model. Turbulence generating grids of parallel rods of diameter, 2.86 cm, 1.59 cm and 0.95 cm, were placed upstream of the heat transfer model in horizontal and vertical orientations to generate freestream turbulence with different orientations of vortical structures. The rods in horizontal orientation were perpendicular to the stagnation line and those in vertical orientation were parallel to the stagnation line of the heat transfer model. The distance between the grid and heat transfer model was varied from 25 to 125 rod diameters. The grids with rods in the horizontal orientation, where the primary vortical structures are expected to be perpendicular to the stagnation line, result in higher heat transfer than with the grids where the rods are in the vertical orientation. The difference in heat transfer with the two grid orientations decreases with increasing grid-to-model distance for a given rod-grid. The difference also decreases with decreasing rod size for a given normalized grid-to-model distance. For the 2.86 cm rod-grid, the difference in heat transfer augmentation between horizontal and vertical grid-orientations is highest at the stagnation line and decreases with streamwise distance. This difference, however, remains fairly constant over the whole stagnation region for the 1.59 cm and 0.95 cm rod-grids.

Theoretical Post-Dryout Heat Transfer Model

2018 ◽  
Vol 1 (1) ◽  
pp. 142-150
Author(s):  
Murat Tunc ◽  
Ayse Nur Esen ◽  
Doruk Sen ◽  
Ahmet Karakas
Keyword(s):  
Heat Transfer ◽  
Droplet Diameter ◽  
Heat Transfer Model ◽  
Transfer Model ◽  
Operating Pressure ◽  
Vertical Pipe ◽  
Two Phase ◽  
Experimental Values ◽  
Reactor Operating ◽  
Coolant System

A theoretical post-dryout heat transfer model is developed for two-phase dispersed flow, one-dimensional vertical pipe in a post-CHF regime. Because of the presence of average droplet diameter lower bound in a two-phase sparse flow. Droplet diameter is also calculated. Obtained results are compared with experimental values. Experimental data is used two-phase flow steam-water in VVER-1200, reactor coolant system, reactor operating pressure is 16.2 MPa. On heater rod surface, dryout was detected as a result of jumping increase of the heater rod surface temperature. Results obtained display lower droplet dimensions than the experimentally obtained values.

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